煤系致密砂岩气渗流机理实验模拟研究——以四川盆地上三叠统须家河组煤系致密砂岩气为例

中国含（油）气盆地广泛发育与煤系烃源岩共生或伴生的致密砂岩气，以四川盆地须家河组和鄂尔多斯盆地上古生界最为典型。受煤系烃源岩大范围面状蒸发式排烃和低缓构造背景影响，致密砂体内气体运移聚集过程中水动力和浮力作用相当受限，在这种低渗低速条件下，非达西渗流特征非常明显，形成气—水混杂的含气区。致密砂岩气驱水模拟实验中，渗流曲线形态主要受岩心渗透率大小的影响，渗透率值越低，则启动压力梯度越大，非达西现象愈加明显。致密砂岩注气驱水实验过程中，岩心的最大含气饱和度一般小于50%，主要分布在30%～40%之间，含气饱和度平均值为38%左右，与地下岩心所在气层的实际含气饱和度比较相近。岩心含气饱和度与渗透率呈较好的对数正相关关系，相关系数为0.891 5。致密砂岩气体单相渗流过程中，由于存在气体渗流的“滑脱效应”，低速非达西渗流特征异常明显，存在“拟初始流速V_d”。 单相气体渗流曲线形态特征主要受岩心渗透率及环压大小控制，渗透率值愈小或者环压值愈大，则非线性段越长，临界压力越高，启动压力梯度越大（0.02~0.08MPa/cm），拟初始流速则越大，非达西渗流特征越明显。致密砂岩气渗流机理研究表明，储层渗透率越低，启动压力越大，流速越慢，天然气运聚效率和含气饱和度较低。针对煤系致密砂岩气运聚机理实验室模拟研究，为揭示致密砂岩气富集规律和评价选区，同时为开发机理研究提供理论基础。

The experiment simulation study on gas percolation mechanisms of tight sandstone core in coal measure strata:A case study on coal-measure tight sandstone gas in the Upper Triassic Xujiahe Formation,Sichuan Basin,China

Tight sandstone gas from coal-measure source rocks is widespread in China,and is most characterized by the Xujiahe Formation of the Sichuan Basin and the Upper Paleozoic of Ordos Basin.Coal-measure source rocks expelled hydrocarbon evaporatively.Under the setting of gentle structure,the gas migration-accumulation in tight sandstone is featured by restricted hydrodynamic and buoyance.Under the condition of low permeability and speed,non-Darcy flow is quite obvious,forming gas-water mixed mid-high water-bearing gas zone.In the water drive experiment,the shape of percolation flow curve is mainly influenced by core permeability:The lower the permeability,the higher the starting pressure gradient,and the more obvious the non-Darcy phenomenon.In the gas drive water experiment of tight sandstone,the maximum core gas saturation is generally less than 50% (ranging from 30% to 40% and averaging at 38%),similar to the actual gas saturation of the gas zone in the subsurface core.The core gas saturation and the permeability have correlative relationship,with correlation coefficient of 0.891 5.In the single-phase flow of tight sandstone gas,low-velocity non-Darcy percolation is obvious and proposed initial flow velocity (V_d) exists due to the slippage effect of gas flow.The shape of percolation flow curve in single-phase gas is primarily controlled by core permeability and circling pressure:the lower the permeability or the higher the circling pressure,the higher the starting pressure (0.02-0.08MPa/cm),proposed initial flow speed,square gradient of the critical pressure;the nonlinear section would also be longer and the non-Darcy flow would be more obvious.In general,tight sandstone gas seepage mechanism study showed that the lower the reservoir permeability,the bigger the start-up pressure,the slower the flow velocity.The efficiency of natural gas and gas saturation is low.The laboratory simulation research on coal-measure dense sandstone migration accumulation mechanism,provides a theoretic foundation for revealing the tight sandstone gas enrichment regularity,evaluation of prospecting area and the study of development mechanism